another impedance question

[Leo_Gnardo]

So what I'm feeling here is, I don't know why I am getting this unexpected result, and so far no one else does either it seems.

Could it be the connector? I found a quarter-inch jack gone spectacularly bad once in a crustomer's single-18 JBL cab. The power amp he used to drive it went into protect mode when he tried to use it. I measured one ohm impedance by plugging in a speaker cable and measuring across the wires. Popped the back off, the speaker alone measured about 6 ohms, what you'd expect. The speaker jack as it turned out had been charred by sending an awful lot of power thru that jack, and it was the obvious cause of the problem once we knew where to look. So . . . unlikely as it is, don't rule it out.

[Chuck H]

If all speakers on their own are 14R and two in series measures lower than the sum of two and then two series pairs parallel measures lower than the division of two, what I see is that additional loading is lowering the measurement. So I'll back Dude and suspect meter loading.

[g1]

I'd agree with the meter idea, but he did try another cab and it measured 13 ohms.
I guess the next thing would be to check the individual speakers in that other cab. for comparison.

[J M Fahey]

Main thing is that the 1 or at most 2 ohm error we are seeing is in the order of magnitude of the meter or measuring technique error, not larger, thatīs why I said donīt worry.

Nobody asked or answered what does the meter show when both leads are touching.
I very much doubt it shows 0 .

My cheap meters always show between 0.3 and 0.4 ohm when new out of the box and with fresh battery up to 1.6 or 1.8 ohm inn the pitiful state they usually are.

It is not an alectronic or digital problem but the very real resistance of: probes, cables, banana plugs/jacks, and something usually ignored: rotary/pushbutton switches inside the meter.

When I short abused meter leads, first I unplug and reseat banana plugs, twist them around to scratch surface grime, and rotate selector switch back and forth a couple times, for same reason, that alone cuts 0.3 to 0.4 ohm of the value displayed

And another detail: parasitic/residual resistance (what I mention above) "adds but does not multiply" meaning, in a made up example but not far from what we see here:
imagine a real cheaty "16 ohm" speaker with 10 ohm DCR (I have measured 5 ohm in some Eminence and 5.5 ohm in EV , both nominally 8 ohm, so thatīs not an overstatement at all) and a crummy 2 ohm internal resistance meter.

A single speaker will show 12 ohm.

IF you take that at face value, you are in for a couple little surprises:
* 2 speakers in series will NOT show 24 ohm but 22 .
* two speakers in parallel will NOT show 6 ohm but 7 .

Admittedly, a Fluke anything will have less parasitic resistance than my cheap yellow $10 multimeters, but it will still have some.

The answer is, of course, "4 wire ohmmeters" which is a very inexpensive solution that surprisingly is not more popular.

Which is nothing nore that usin 4 wires: 2 to send constant current to the tips, so parasitic resistance becomes irrelevant, and 2 wires which carry no current, so no voltage drop, to carry voltage drop across measured object back to meter board.

Total manufacturing cost increase?: about 2 bucks.

Iīm very lazy, because I should have converted my meters to 4 wire long ago.

[jmaf]

Also note that lots of Celestions measure lower.

8 ohms Celestions usually measure 6.x ohms at 1 khz on my LCR bridges, so even considering the 80% DCR component in most impedance, even at AC 1 khz some speaker brands measure lower, cuz guitar speakers aren't hi-fi and not precisely 8 ohms at 1khz, they actually get some tone shaping magic in them.

Like JMFahey said don't overthink it.

[Old Tele man]

That's why the "≈" symbol often replaces the "=" symbol.

[Randall]

As I said, we had two meters, my fluke which is new and measures 0.1 with tips shorted, and his generic which measured maybe half an ohm higher readings than mine, so I don't think it's that. I don't understand it, but if he plays the cab and it sounds good, than I will call it good.

One thing I just noticed, this new Fluke 101 has an odd way of reading resistance. When I short the tips it jumps around a bit then settles to 0.9 and slowly counts down to 0.1 or 0.2, but it takes like 12 seconds. That seems odd and it probably skewed some of my measurements, and I might chalk it up to that except we had two meters and they both measured 10 point something on the NEW jack I installed.

[Leo_Gnardo]

we had two meters and they both measured 10 point something on the NEW jack I installed.

O-Tay, can't blame a dodgy jack then. The mystery continues...